1. Field of the Invention
The present invention relates to a silver halide color photographic lightsensitive material. More particularly, the present invention relates to a silver halide color photographic lightsensitive material which is highly sensitive, is excellent in graininess and exhibits high sharpness.
2. Description of the Related Art
With respect to the silver halide color photographic lightsensitive material, further sensitivity enhancement is being urged for increasing the user benefit of color negative films. Especially in recent years, the regular use of highly sensitive films of 800 or higher specific photographic speed (ISO speed) is being promoted in accordance with the penetration of compact cameras with zooming capability and lens-equipped films which enable readily and easily coping with various exposure conditions.
This film sensitivity enhancement realizes an expansion of the photographing range of lightsensitive materials to, for example, photographing without the use of stroboscopic flash in dark rooms, fast-shutter photographing with the use of telephoto lens like sports photography, photographing requiring long-time exposure like astronomical photography, etc. Thus, the users can have tremendous benefits therefrom. Therefore, the sensitivity enhancement of films is one of everlasting themes to be tackled in this industry.
The conventional high-speed films have been those whereby only images of low grade far above the threshold of user's tolerance can be obtained as a result of the pursuit of sensitivity enhancement. Therefore, the users have been forced to choose between speed and image quality, and often the user's choice has resulted in having to take image quality rather than speed.
For enhancing the sensitivity of lightsensitive materials, it is old trick in this industry to increase the size of silver halide grains as photosensitive elements and further simultaneously employ other sensitivity enhancement technologies.
The sensitivity enhancement can be realized to a certain level by an increase of the size of silver halide grains. However, as long as the content of silver halides stays constant, the size increase would inevitably lead to a decrease of the number of silver halide grains, namely, a decrease of the number of development initiation centers and would consequently cause a disadvantage of extreme graininess deterioration.
Moreover, a design intended to increase the number of silver halide grains per area, namely, an increase of the amount of silver halides used in lightsensitive material coating would invite such a problem that deteriorations of photographic performance, such as fog increase, sensitivity lowering and graininess deterioration, occur during the storage of lightsensitive material after production and before use thereof.
Meanwhile, recently, there has been disclosed a technology of achieving a sensitivity enhancement without detriment to graininess by incorporating a compound, the compound having at least three heteroatoms that do not react with oxidizing developing agents, in a silver halide photographic lightsensitive material (see, for example, Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-) 2000-194085).
Tabular silver halide grains have been employed for the sensitivity enhancement of lightsensitive materials. With respect to the tabular silver halide grains, not only have processes for producing the same and technologies for use thereof been disclosed but also the advantages, such as improvements of the relationship of speed/graininess including an improvement of color sensitization efficiency by spectral sensitizing dyes, are known (see, for example, U.S. Pat. No. 4,434,226).
Extensive studies have been conducted for the performance enhancement of these advantageous tabular grains. Tabular grains of large equivalent circle diameter and reduced thickness are advantageous for the sensitivity enhancement from the viewpoint that spectral sensitizing dyes can be adsorbed thereto in greater amounts. The thinner the tabular grains, the greater the amount of adsorbed dyes. However, practically, attaining a sensitivity enhancement effect conforming to an increase of the amount of adsorbed sensitizing dyes becomes difficult in accordance with the reduction of grain thickness. As a reason therefor, there can be mentioned, for example, the influence of unfavorable electron trap within grains. Technologies for attaining sensitivity enhancement by removing the electron trap are disclosed (see, for example, JP-A-2001-281778).
However, even when these technologies are employed, there occurs such a problem that the introduction of dislocation lines that are effective in sensitivity enhancement becomes difficult in accordance with the reduction of the thickness of tabular grains. Thus, the intended sensitivity enhancement has not been attained. Therefore, there is a demand for a further technology attaining sensitivity enhancement.
On the other hand, it is known that the sharpness of lightsensitive materials can be improved by reducing the thickness of the protective layer thereof. Further, it is described that the sharpness of lightsensitive materials can be improved by reducing the thickness thereof with the use of tabular grains (see, for example, JP-A-5-034857). However, the light scattering by tabular grains per se is increased in accordance with the reduction of the thickness of tabular grains. Consequently, there has occurred such a problem that the reduction of the thickness of tabular grains employed rather leads to a deterioration of the sharpness of lightsensitive materials.
Under these circumstances, it has been difficult to obtain a lightsensitive material that is highly sensitive by virtue of the advantage of tabular grains and simultaneously exhibits high sharpness.